Hydroacoustic oscillator techaniques



g- 11, 1964 J. v. BOUYOUCOS HYDROACOUSTIC OSCILLATOR TECHNIQUES Filed May 5, 1962 IN VEN TOR. JOHN V. BOUYOUCOS ATTORNEY PUMP United States Patent 3,143,999 HYDRGACOUSTIC OSCILLATOR TECHNIQUES John V. Bouyoueos, 10 Blossom Circle E., Rochester 10, N.Y. Filed May 3, 1962, Ser. No. 192,274 Claims. (U. 116-137) This invention relates to self-excited hydroacoustic transducers and, more particularly, to means for enhancing the power conversion performance of hydroacoustic oscillators by proper use of forces resulting from fluid momentum transfer effects.

In U.S. Patent 2,792,804 of John V. Bouyoucos and Frederick V. Hunt, there are described several embodiments of acoustic vibration generators of the self-excited oscillator type which convert hydraulic flow energy into acoustic energy when a fluid medium flowing under pressure in a closed path is modulated regeneratively by valving means. The valving means may move back and forth within a stationary port structure which cooperates with the valving means to modulate flow through orifices defined at the opposing ends of the valving means, or through a single orifice, in the case of single-ended switching. In this Way, the fluid passing into and from oscillator cavities disposed in the fluid path is alternately accelerated and decelerated, causing pressure variations within the cavities. By proper design, these pressure variations may be made to react upon the valving means in such phase relative to the motion of the valving means as to sustain the valving action. These pressure variations give rise to acoustic energy which may be extracted from at least one of the oscillator cavities.

One of the factors limiting the maximum theoretical efficiency of power conversion of prior hydroacoustic transducers stems from the loss of kinetic energy associated with the jet which is developed on the downstream side of the switching orifice. The kinetic energy of a discharge jet is always finite and is worthwhile recovering as useful energy. As long as this kinetic energy is left to become dissipated in turbulence in the discharge cavity, it is wasted energy. By proper modification of the valving element, it is possible to controllably recover at least a portion of the discharge kinetic energy in order to increase the overall power conversion efficiency of the hydroacoustic oscillator.

In addition to the regenerative pressure forces that can exist upon the valve by virtue of the gross effects of flow modulation, already mentioned, further forces may be applied to the valve as a result of fluid momentum transport effects in the immediate vicinity of the valving region. There is, for example, a static fluid flow force that tends always to close a valve. This steady state force is proportional to the product of the density of the fluid, the rate of flow through the orifice and the component of velocity of fluid flowing through said orifice along the axis of valve motion. There is, furthermore, a dynamic flow force proportional to the rate of change of flow of the fluid through the orifice in a direction which depends upon the direction of flow of the fluid. By means hereafter to be described, it is possible to make use of the forces exerted on said valve immediately downstream of the orifice as a consequence of the dynamic flow through the orifice to enhance or reinforce the motion of the valve accomplished by the effects of flow modulation. The effect of said enhancement may result not only in increased efliciency of power conversion, but also in increased power handling capability.

In addition to providing a regenerative valving ar- I rangement, it may be further desirable to stabilize statically the aforesaid valve.

This can be accomplished,

3,143,999 Patented Aug. 11, 1964 in the case of the single-ended oscillator, by the balancing of the closing force arising from the efllux of momentum through the orifice with an opening force of equal magnitude by designing the opposite end faces of the valve of different diameters. The desired balanced condition may be shown to attain when the dilference in diameter of the opposite ends of the valve is substantially equal to the desired orifice spacing when the valve is in the equilibrium or center position. In the push-pull oscillator, the closure forces on opposite sides of the valve are oppositely directed. Thus, the conditions for static balance are achieved without the necessity of resorting to unequal valve end faces.

FIG. 1 is a central cross-sectional view of a hydroacoustic oscillator in accordance with the invention;

FIG. 2 is an enlarged view showing details of the valving means of FIG. 1; and

FIG. 3 is a view illustrating a further embodiment of the invention.

Referring now to FIGS. 1 and 2, a single-ended hydroacoustic oscillator 10 is illustrated which takes advantage of both the static and dynamic flow forces originating in the immediate vicinity of the valving orifice. The oscillator 10 includes a valve 12 axially movable with respect to a stator port assembly 14. The oscillator further includes a pair of oscillator chambers 15 and 16 communicating with opposite faces 18 and 19 of valve 12. As will be explained subsequently, the diameter of end face 19 is greater than that of end face 18. An orifice 20 is provided by the land portion 22 of port assembly 14 and the end portion 24 of valve 12. An axial spacing x is maintained between the valve and the stator port assembly in the null or equilibrium position of the valve. A fluid under pressure from a hydraulic pump 25 enters the housing 26 through conduit 27 and passes through pressure release cavity 21 and inlet line 28 into chamber 15. The volume of cavity 21 is considerably larger than that of chamber 15. The fluid next passes through orifice 20 into the region 30 bounded in part by opposite lands 24 and 31 of valve 12. The fluid then flows into the discharge region 35 and outlet line 37 back to fluid pump 25. In order to equalize the static pressures in chambers 15 and 16, a hydraulic short circuit is provided by means of loop 40 interconnecting the two chambers. Whereas loop 4!) enables the static pressure in chambers 15 and 16 to beequal, the acoustic impedance of loop 40 should be sufliciently high at the operating frequency so that negligible acoustic flow exists within the loop.

The oscillator operating frequency is chosen so that it is below the resonant frequency of the acoustic circuit of the valve including the stilfness of chamber 16 and the mass of valve 12, whereupon the valve is stiffnesscontrolled and moves in phase with the force applied to surface 18 of the valve. If the valve 12 should be subjected to an incremental oscillation about its equilibrium position, resulting, for example, in an instantaneous displacement of the valve away from acoustic chamber 15, there will result a reduction of the fluid flow through orifiice 20, accompanied by an increase of pressure in chamber 15. This increase in pressure causes a force to be exerted against the exposed face 181 of valve 12 in a direction such as to assist in closure of orifice 20. If, on the other hand, the valve should tend to open, i.e., be displaced toward acoustic chamber 15, there will be an increase in fluid flow through orifice 20 and a decrease in pressure in chamber 15. The decrease in pressure causes a force to be exerted upon the face 18 of valve 12 such as to assist in opening orifice 20.

The regenerative forces above described can result in a self-excited oscillation of the system at a frequency for which the inertance of the inlet line 28 is in parallel resonance with the net acoustic stiffness provided by the parallel combination of the stiffness of the fluid in chamber and the stiffness presented by the face 18 of the valve backed by the fluid in chamber 16.

The acoustic energy generated within chamber 15 is shown to lie/coupled to a radiating piston 45 which may be resiliently mounted to the oscillator housing 26. Other forms of coupling devices may, of course, be employed.

Consider now the forces exerted upon valve 12 owing to the momentum transport effect. As the valve 12 moves toward chamber 15, the orifice opening increases and the fiow of fluid therethrough accelerates. A dynamic pressure differential is thereby created within region 30 wherein the pressure is higher in the vicinity of orifice than in the vicinity of the exit region 35. The pressure of the fluid within region 35 at a point remote from orifice 20 remains substantially at the return pressure "of the fluid system. In other words, there is a resulting force exerted on the surfaces 32 and 33 of valve 12 which is in the same direction as the motion of the valve. As the valve 12 moves 'toward chamber 16, the orifice 20 begins to close, the flow of fluid decelerates and ,a pressure differential is created in region 35 such that thepressure is higher in the vicinity of exit 35 than in the vicinity of orifice20. A net dynamic force then is exerted on valve surfaces 32 and 33 which again aids the movement of thevalve. The dynamic force exerted on the valve can be shown to be in phase with the valve velocity. As a result, a negative resistance appears in the valve circuit which helps to accentuate the regenerative behavior of the valve, thereby aiding the power conversion process. p

In addition to providing negative damping, essential for a regenerative valving arrangement, it is also desirable to stabilize the valve statically. This may be achieved by making the diameter of face 19 of the valve 12 larger than the diameter of face 18 to create a static opening force of such magnitude as to balance the closing force arising from the efiiux of momentum through the orifice 20. The static axial flow on valve 12 equals the axial component of the net rate of efliux of momentum through the boundary of region 35. In practice/the area of orifice 20 is considerably smaller than the exit area at the boundaries of regions 35 and 37. Since the velocities are inversely proportional to the areas, the efllux ofmomentum from region 35 into region 37 is negligible compared to the influx of momentum at orifice 20. The closing force F is given by F Qv, where p is the density of the fluid, Q is the rate of flow of fluid through the orifice 20, and v is the axial component of velocity of the flow of fluid passing through the orifice. The velocity v may be given by 11 01, oos0 (l) where C is the velocity coefficient, 6 is the angle which the axis of the stream makes with the valve axis and AP is the difference between the upstream and downstream pressure. The rate of flow Q is given by F (C Wx Cu cos 0 =2C CuxAP cos 0 It is evident that the closing force is proportional to the product of the displacement x and the pressure differential AP.

The closing force F creates a stiffness force in phase with the position in the valve and always tends to close the valve orifice, regardless of the direction of fluid flow therethrough.

The axial force exerted on the piston which tends to cause the valve to open will now be considered. The fluid loop 40 constituting a static hydraulic short circuit places both chambers 15 and 16 at the same internal pressure. Since the area of valve face 19 is greater than that of valve face 18, there will be a net opening force to the right. This opening force may be given by where A and A represent the area of faces 19 and 18, respectively, of valve 12. w v I For equilibrium, the closing force F and the opening force F are equal; that'is,

zc 'Wx cos 0=A A s It will be noted that this equation is not dependent upon the quantity AP. For practical values of operation and using metering orifice of rectangular configuration, C C =O5 and cos 0 0.5. v If r; and r are the radii of respective end faces 19 and 18 of valve 12, Equation 5 can be written wr x=1r(r -r (6) The difference between the two radii r and r may be represented by Ar and is small compared to either r or r In other words,

r =r i+Ar (8) Rewriting Equation 7 and solving for x,

xz 22M (9) Thus, the difference in diameter of the two opposite faces 18 and 19 of the valve 12 is substantially equal to the desired orifice spacing. By using unequal areas on the valve faces, it is possible to obtain a condition'of force balance and an equilibrium orifice spacing independent of pressure.

In the double-ended design wherein fluid flows through orifices at both ends of the valve, the closing forces on opposite faces of the valve are oppositely directed'and tend to cancel one another, thereby tending to stabilize the null position automatically. In such a case, a difference in area of opposing valve faces would, of course, be undesirable.

Referring to FIG. 3, a hydroacoustic oscillator 10' is shown which embodies a push-pull valving configuration. In this oscillator, fiuid flows into each of the oscillator chambers and 116 and out through orifices 36 and 39 to a discharge chamber 92 and outlet 51 to the return side of a fluid pump 121. The valve 112 includes an annular projecting 'section' 50 extending radially from the body of valve 112 which is intended to intercept a portion of the energy of the orifice discharge in such a phase relation as to enhance the valve motion, thereby to aid the power conversion process. This projecting section provides channels 61 and 62' between the faces 71 and 72 of the'projecting section 50 of the moving valve and the juxtaposed surfaces oftheportion 81 and 82 of stator assembly 14, all respectively.

The basic operation of the oscillator is such that, if the massive valve 112 of FIG. 3 should be subjected to an incremental oscillation about its equilibrium position, result ing at some instant, for example, in an incremental displacement of the valve towards chamber 116, a decrease of fluid discharge from chamber 116 will occur, accompanied by an increase in pressure within this chamher; on the other hand, an increase of fluid discharge will occur from chamber 115, accompanied by reduction of pressure therein. The relatively higher instantaneous pressure in chamber 116, coupled with the relatively lower instantaneous pressure chamber 115, provides a net force increment on massive valve 112 which is directed opposite to the above assumed incremental displacement of the valve, or in phase with its acceleration.

An incremental oscillating acceleration of massive valve 112 thus will be accompanied by push-pull pressure changes within chambers 115 and 116 which react upon valve 112 to accentuate the given acceleration. This illustrates the regenerative nature of the valving action. If the losses in the acoustic circuit of the generator are not too high, this regenerative feature will permit oscillations to build up and to be sustained at a frequency for which the acoustic reactance, seen looking into chambers 115 and 116 from the orifices 36 and 3% is equal but of opposite sign to the acoustic reactance presented by the valve. The acoustic energy generated within chambers 115 and 116 may be coupled by means of respective piston-type radiators 125 and 126 to external load means.

The extraction of energy from the discharge jet to aid the valve oscillator will now be analyzed. As the valve 112 moves toward chamber 116, the area of annular orifice 39 decreases and the fluid flow therethrough is decelerated. Simultaneously, the massive fluid column flowing radially from the downstream side of orifice 39 through channel 61 to the discharge chamber 92 is decelerated. This deceleration of flow in channel 61 is accompanied by a reduction of pressure in channel 61 with respect to the pressure in the discharge chamber 92.

At the same time that the area of annular orifice 39 is decreasing, owing to motion of valve 112 toward chamber 116, annular orifice 36 is increasing, and the fluid flow therethrough is accelerated, resulting in an acceleration of the massive fluid column bowing radially from the downstream side of orifice 36 through channel 62 to the discharge chamber 92. This acceleration of flow in channel 62 is accompanied by an increase in pressure in channel 62 with respect to the pressure in discharge chamber 92.

Thus, accompanying a motion of the valve toward chamber 116, there will be an increase in pressure in channel 62 and a decrease in pressure in channel 61, with respect to discharge chamber 92, resulting in a net force on the projecting faces 71 and 72 of annular projecting section Stl of the valve 112 directed toward chamber 116. It is evident that a motion of valve 112 toward chamber 115, on the other hand, will result in a net force on the projecting faces 71 and 72 of annular projecting section 50 of the valve directed toward chamber 115.

It is to be noted that the fluid volume velocity through orifices 36 and 39 will be approximately in phase with valve displacement, if positive valve displacement is taken in the direction of orifice opening. Since, however, the pressure variations in channels 61 and 62 are in phase with the acceleration of the channel flow, the pressure variations must be in phase with the valve velocity. But this is to say that the pressure variations arising from the acceleration and deceleration of the fluid contained in the discharge jet within the channels 61 and 62 do pushpull work upon the valve to aid its motion. Looked at from another point of view, the valve sees a negative resistance arising from energy extracted from the discharge stream.

In addition to a negative resistance, the valve can see an additional mass loading due to the fluid that is squeezed out of the channels 61 and 62 as the faces 71 and 72 of the projecting section 50 move relative to the juxtaposed surfaces of the portions 81 and 82 of the stator assembly 14.

In summary, then, the presence of projecting section 50 on the valve 112 can provide a negative resistance to valve motion arising from the acceleration and deceleration of the discharge jet as controlled by the instantaneous orifice spacings. In "addition, the squeezing of fluid in and out of channels 61 and 62 due to valve motion relative to the stator assembly provides additional mass loading upon the valve.

The negative resistance observed can aid the power conversion process since, in eflect, energy contained within the discharge jet is now being recovered as useful work, and is not being Wholly dissipated in turbulence in the discharge channel. The eft'ect of the additional mass loading upon the valve will act to lower slightly the oscillation frequency from that to be observed in the absence of projecting section 50.

What is claimed is:

1. In an acoustic vibration generator comprising a port structure partially bounding a pair of chambers containing a fluid under pressure, said port structure further containing a discharge chamber connected externally to the low pressure side of a fluid source, a fluid control valve movable in response to pressure variations within said chambers to provide variable orifice means for modulating the flow of fluid through said chambers and to produce pressure variations therein, said valve being driven relative to said port structure in consequence of said pressure variations to sustain the flow modulation, said valve having means projecting therefrom for at least partinually defining a discharge region intermediate said discharge chamber and said orifice means for conveying fluid passing through said orifice means into said discharge chamber, the movement of fluid within said discharge region providing a pressure gradient within said discharge region producing a net force upon said projecting means aiding the movement of said valve.

2. In an acoustic vibration generator comprising a port structure partially bounding a pair of chambers containing a fluid under pressure, said port structure further containing a discharge chamber connected externally to the low pressure side of a fluid source, a fluid control valve movable in response to pressure variations Within said chambers to provide variable orifice means for modulating the flow of fluid through said chambers and to produce pressure variations therein, said valve being driven relative to said port structure in consequence of said pressure variations to sustain the flow modulation, said valve having means projecting therefrom into said discharge chamber for at least partially defining a discharge region intermediate said discharge chamber and said orifice means for conveying fluid passing through said orifice means into said discharge chamber, the movement of fluid within said discharge region providing a pressure gradient within said discharge region producing a net force upon said projecting means aiding the movement of said valve.

3. In an acoustic vibration generator comprising a port structure partially bounding a pair of chambers containing a fluid under pressure, said port structure further containing a discharge chamber connected to the low pressure side of a fluid source, a fluid control valve movable in response to pressure variations within said chambers to provide variable orifice means for modulating the flow of fluid through said chambers and to produce pressure variations therein, said valve being driven relative to said port structure in consequence of said pressure variations to sustain the flow modulation, said valve including two oppositely disposed end portions at least partially defining a discharge region intermediate said discharge chamber and said orifice means for conveying fluid passing through said orifice means into said discharge chamber, the movement of fluid Within said discharge region providing a pressure gradient within said discharge region producing a net force upon said end portions aiding the movement of said valve.

4. In an acoustic vibration generator comprising a port structure partially bounding a pair of chambers containing a fluid under pressure, said port structure further containing a discharge chamber connected to the low pressure side of a fluid source, a fluid control valve movable 7 in response to pressure variations within said chambers to provide variable orifice means for modulating the flow of fluid through said chambers and to produce pressure variations therein, said orifice means having a predeter: mined longitudinal'opening when said valve is in the equilibrium position, said valve being driven relative to said port structure in consequence of said pressure variations to sustain the flow modulation, said valve including two oppositely disposed end portions having diameters which differ by the amount of opening of said orifice means, said valve end portions at least partially defining a discharge region intermediate said discharge chamber and said ori fice means for conveying fluid passing through said orifice means into saiddischarge'chamber, the movement of fluid within said discharge region providing a pressure gradient 'a fluid under pressure, said port structure further containing a discharge chamber connected externally to the low "pressure side of a fluid source, a fluid control valve movable in response to pressure vibrations within said chambers to provide variable orifice means for modulating the flow of fluid through said chambers and to produce (pressure variations therein, said valve being driven relative to said port structure in consequence of said pressure variations to sustain the flow modulation, said valve in:

cluding a radially projecting portion forming with said port structure a pair of narrow fluid channels for discharging said fluid passing through said orifice means in said discharge chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,618,982 'Hahneman'n'et al Mar. 1, 1927 2,164,858 West July 4, 1939 2,693,944 Fowle Nov. 9, 1954 2,792,804 Bouyoucos'et a1 May 21, 1957 2,859,726 Bouyoucos et'al Nov. 11, 1958 I 3,004,512 Bouyoucos et al. Oct. 17, 1961 

1. IN AN ACOUSTIC VIBRATION GENERATOR COMPRISING A PORT STRUCTURE PARTIALLY BOUNDING A PAIR OF CHAMBERS CONTAINING A FLUID UNDER PRESSURE, SAID PORT STRUCTURE FURTHER CONTAINING A DISCHARGE CHAMBER CONNECTED EXTERNALLY TO THE LOW PRESSURE SIDE OF A FLUID SOURCE, A FLUID CONTROL VALVE MOVABLE IN RESPONSE TO PRESSURE VARIATIONS WITHIN SAID CHAMBERS TO PROVIDE VARIABLE ORIFICE MEANS FOR MODULATING THE FLOW OF FLUID THROUGH SAID CHAMBERS AND TO PRODUCE PRESSURE VARIATIONS THEREIN, SAID VALVE BEING DRIVEN RELATIVE TO SAID PORT STRUCTURE IN CONSEQUENCE OF SAID PRESSURE VARIATIONS TO SUSTAIN THE FLOW MODULATION, SAID VALVE HAVING MEANS PROJECTING THEREFROM FOR AT LEAST PARTINUALLY DEFINING A DISCHARGE REGION INTERMEDIATE SAID DISCHARGE CHAMBER AND SAID ORIFICE MEANS FOR CONVEYING FLUID PASSING THROUGH SAID ORIFICE MEANS INTO SAID DISCHARGE CHAMBER, THE MOVEMENT OF FLUID WITHIN SAID DISCHARGE REGION PROVIDING A PRESSURE GRADIENT WITHIN SAID DISCHARGE REGION PRODUCING A NET FORCE UPON SAID PROJECTING MEANS AIDING THE MOVEMENT OF SAID VALVE. 